1. Field of the Invention
The present invention relates to a thin sheet-shaped semiconductor device and a method for producing it. More particularly, the present invention relates to a portable type thin sheet-shaped semiconductor device, such as a non-contact type IC card wherein semiconductor functional components are fully embedded in a resin, and relates to a method for producing it.
2. Description of the Related Art
FIGS. 51 and 52 are a plan view and a side elevational view of a conventional thin sheet-shaped semiconductor device of integral type such as, for example, an IC card (referred to as "IC card" hereinafter). Referring to these figures, functional parts of the IC card such as a packaged IC 3 (referred to as "IC" hereinafter) are mounted on a circuit board 2. The circuit board 2 is surrounded by a frame 7 which is provided on its inner surface with projections (referred to as "ribs" hereinafter) which contact the outer edge of the circuit board 2. The circuit board 2 and the frame 7 are integrated with each other by a forming resin 8 filling the interior of the frame 7, thus realizing an IC card having sufficient strength.
A conventional thin sheet-shaped semiconductor device is typically configured in such a manner described above. This example shown in FIGS. 51 and 52 is a type generally called a non-contact IC card which has no electrical contacts for external interconnections. This type of a thin sheet-shaped semiconductor device is produced as follows. First, functional components such as an IC 3 are mounted on the circuit board 2 such as a lass-filled epoxy printed circuit board. Then, the side of the circuit board 2 on which no components are mounted is covered with a thin plate (surface material) 5 which acts as a case material. Furthermore, the edge portion of the circuit board 2 is pressed against a rib 7a, and the molding resin 8 is filled in the inside of the frame 7 such that the side of the circuit board 2 having the components is covered with the molding resin 8 and such that the thin plate 5, the circuit board 2, and the frame 7 are molded into a single piece with the molding resin 8.
FIGS. 53 and 54 are a plan view and a cross-sectional side view, respectively, of another type of conventional IC card. As shown in these figure, a circuit board 2 on which functional components are mounted is contained in a case 13 made of, for example, plastic. The circuit board 2 is a glass-filled epoxy printed circuit or the like. Functional components such as an IC 3, a battery (not shown) serving as a power source, and other components are mounted on the circuit board 2 wherein these components are connected to an electrical interconnection circuit (not shown) formed on the circuit board 2. The circuit board 2 with these components is placed between a pair of case halves 13a and 13b. These case halves 13a and 13b are bonded to each other. Thus, a complete IC card 1 is obtained.
Then, a design is added to the surface of the exposed side of the thin plate 5 and/or to the surface of the molding resin of the IC card 1. The design is added to the surface of the molding resin after the molding of the resin is complete by printing technology such as silk screen printing or by thermal transfer or by sticking a printed seal such as a tack seal on the surface.
In the thin semiconductor devices described above, it is important to provide representations of the product type, functions, notes, and other designs on the surface of the card. These representations should be clear and beautiful in a sense of art. In the conventional ICs, a design is printed or thermal-transferred on the surface of the molded material, or otherwise a label is stuck on it. When printing or thermal transfer is carried out on such an integrally molded card as shown in FIGS. 51 and 52, applicable methods of printing are limited, because the flatness of the surface of the molding resin is slightly degraded due to thermal shrinkage. This degradation of the flatness occurs because there is local variation in the thickness of the molding resin depending on whether there exists a component embedded inside the molding resin.
On the other hand, in such a thin sheet-shaped semiconductor device as shown in FIGS. 53 and 54, although functional components are contained in a plastic case having flat surfaces, the existence of the free space in the case often introduces deformation in the card itself, which results in the difficulty in printing. In particular, this problem is serious when the printing is performed by means of thermal transfer.
The common problems for both of the above cases are that it is difficult to perform printing on a molded surface due to a problem associated with adhesion properties of printing ink which occurs due to a mold release agent required for the molded resin 8, and that in the case of thermal printing, heat generation during the thermal printing leads to bowing of the IC card 1. In addition, printing must be carried out individually for each IC card 1 having a significantly large thickness, which results in problems associated with productivity.
There are known methods for producing an IC card in which electronic components are embedded in such a manner that there is no free space within the card. One of such methods is disclosed in Japanese Patent Laid-Open No. 63-257694. In this known method, a thin sheet-shaped semiconductor device is produced as follows. As shown in FIG. 55, a module 16 including functional components is set in a mold 22, and a thermoplastic resin is injected into the mold 22 through an injection inlet 23 so as to mold the module 16 with the thermoplastic resin. In this way, a complete IC card is obtained in which the module 16 is embedded in an IC card body in an integral form. In this method of producing an IC card, terminals for external interconnections (not shown) of the module 16 embedded in the IC card are exposed to the outside of the IC card. The module 16 is fixed in a cavity of the mold 22 with a vacuum fixing technique such that terminals for external interconnections are in contact with the inner surface of the mold 22 and; injection-molding is used to obtain a complete IC card.
FIG. 56 shows another method for producing a non-contact type IC card having no terminals for external interconnections, which is disclosed in Japanese Patent Laid-Open No. 1-241496. In this method, a module 16 including a circuit board 2 on which ICs 3 and a battery 24a are mounted is put in a case 24 for a module 16, then a thermosetting resin to be used as a molding resin is injected into the case 24 through holes 24a provided in one side of the case. Then, the molding resin filling the space in the case 24 is heated to be cured. Thus, the case 24 and the module 16 are molded with the molding resin, and a complete IC card in an integral form is obtained. There is no space remaining in the IC card according to this method. As a result, this card has a mechanical strength strong enough for a person to carry it with him/her.
In the above method for producing a thin sheet-shaped semiconductor device, in which after a module 16 is set in a mold 22, a thermoplastic resin is injected around the module 16 in the case of a non-contact card which has no terminals for external connections, the injection molding is not capable of embedding the whole of module 16 in the resin. One surface must be in contact with the mold 22 so as to fix the module 16 to the mold 22, and this is always exposed to the outside as a surface of a complete IC card. Therefore, this method is not suitable. In some cases, electronic components mounted on the module 16 are damaged by the pressure applied during the injection molding. In particular, in the case of an IC card having a battery 4a, the battery 4a is destroyed during the process of injection molding due to high temperature and high pressure. Thus, this production method cannot be used to embed a battery 4a in an integrated form. Furthermore, when a design is added to the IC card, it is required to print the design on the IC card one at a time, or during the molding process the design is transferred onto the IC card from the inner surface of the mold. Otherwise, a printed label is stuck on the IC card. In any case, it is impossible to obtain high productivity.
On the other hand, in the method in which after a module 16 having functional components is put in a case 24, a S thermosetting resin is filled in the space in the case 24 and cured by means of heating so as to obtain a card in an integrated form, there is little probability that the functional components installed in the card are damaged, because no pressure is applied during the production process. However, when the resin which has been injected into the case 24 is cured, volume shrinkage occurs due to curing-shrinkage, and internal stress is introduced. Because the amount of shrinkage is proportional to the thickness of the resin, variation occurs in the amount of shrinkage from location to location depending on whether a functional component exists at that location or not. As a result, the case 24 is partly deformed inward, so that it is difficult to obtain a flat surface of the IC card. As for addition of a design to the IC card, there are the same problems as in the technology described above.